Power control in schedulable wireless communication terminal

ABSTRACT

A wireless communication entity schedulable in a wireless communication network, including a controller ( 603 ) communicably coupled to a power amplifier ( 608 ), wherein the controller varies a maximum transmit power of the wireless communication entity based on the radio resource assignment information receiver by the radio receiver.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communications, andmore particularly to radio resource scheduling in wireless communicationnetworks, corresponding devices and methods.

BACKGROUND

Some effort is being expended during the specification phase ofcontemporary broadband wireless communication standards such as the 3GPPLong Term Evolution (LTE) project, also referred to as Evolved UMTSTerrestrial Radio Access or E-UTRA, to improve the performance andefficiency of the power amplifier (PA) in mobile terminals or userequipment (UE). Toward this objective, there are a number of keyperformance metrics, but the over-riding goal is to minimize the PApower consumption (or peak and/or mean current drain), cost and thecomplexity required to deliver a given specified conducted power level,for example, +21 dBm or +24 dBm, to the UE antenna.

Generally, the required conducted power level must be achieved within aspecified lower bound on in-band signal quality, or error vectormagnitude (EVM) of the desired waveform, and an upper bound of signalpower leakage out of the desired signal bandwidth and into the receivesignal band of adjacent or alternate carrier receivers. These effectsmay be subsumed into the broader term “waveform quality”.

These problems represent classical PA design challenges, but emergingbroadband wireless networks such as 3GPP LTE must solve these problemsin the context of new modes of system operation. For example, poweramplifier (PA) operation must be optimized while transmitting newwaveform types, including multi-tone waveforms and frequency-agilewaveforms occupying variable signal bandwidths (within a nominalbandwidth, sometimes referred to as a channel or carrier bandwidth).Further, PA performance must now be optimized in a predominantly packetswitched (PS) network where a network entity, such as a base station,schedules multiple wireless communication entities or terminals totransmit simultaneously. PA performance also must be optimized in thepresence of numerous different frequency or spatially adjacent radiotechnologies, including GSM, UMTS, WCDMA, unlicensed transmitter andreceivers, among other radio technologies.

The various aspects, features and advantages of the disclosure willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below. The drawings may havebeen simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary wireless communication system.

FIG. 2 illustrates a wireless communication entity.

FIG. 3 illustrates neighboring communication networks.

FIG. 4 illustrates occupied bandwidth power de-rating values.

FIG. 5 illustrates a radio resource assignment to multiple entities.

FIG. 6 illustrates a power amplifier under control of a controllermodifying the maximum power level.

FIG. 7 illustrates a received signal at a wireless communicationsreceiver, conditioned on the maximum power of a wireless transmitterpower amplifier.

DETAILED DESCRIPTION

In FIG. 1, the exemplary wireless communication system comprises acellular network including multiple cell serving base stations 110distributed over a geographical region. The cell serving base station(BS) or base station transceiver 110 is also commonly referred to as aNode B or cell site wherein each cell site consists of one or morecells, which may also be referred to as sectors. The base stations arecommunicably interconnected by a controller 120 that is typicallycoupled via gateways to a public switched telephone network (PSTN) 130and to a packet data network (PDN) 140. The base stations additionallycommunicate with mobile terminals 102 also commonly referred to as UserEquipment (UE) or wireless terminals to perform functions such asscheduling the mobile terminals to receive or transmit data usingavailable radio resources. The network also comprises managementfunctionality including data routing, admission control, subscriberbilling, terminal authentication, etc., which may be controlled by othernetwork entities, as is known generally by those having ordinary skillin the art.

Exemplary cellular communication networks include 2.5 Generation 3GPPGSM networks, 3rd Generation 3GPP WCDMA networks, and 3GPP2 CDMAcommunication networks, among other existing and future generationcellular communication networks. Future generation networks include thedeveloping Universal Mobile Telecommunications System (UMTS) networks,Evolved Universal Terrestrial Radio Access (E-UTRA) networks. Thenetwork may also be of a type that implements frequency-domain orientedmulti-carrier transmission techniques, such as Frequency DivisionMultiple Access (OFDM), DFT-Spread-OFDM, IFDMA, etc., which are ofinterest for future systems. Single-carrier based approaches withorthogonal frequency division (SC-FDMA), particularly InterleavedFrequency Division Multiple Access (IFDMA) and its frequency-domainrelated variant known as DFT-Spread-OFDM (DFT-SOFDM), are attractive inthat they optimise performance when assessed using contemporary waveformquality metrics, which may include peak-to-average power ratio (PAPR) orthe so-called cubic metric (CM). These metrics are good indicators ofpower backoff or power de-rating necessary to maintain linear poweramplifier operation, where ‘linear’ generally means a specified andcontrollable level of distortion both within the signal bandwidthgenerally occupied by the desired waveform and in neighboringfrequencies.

In OFDM networks, both Time Division Multiplexing (TDM) and FrequencyDivision Multiplexing (FDM) are employed to map channel-coded,interleaved and data-modulated information onto OFDM time/frequencysymbols. The OFDM symbols can be organized into a number of resourceblocks consisting of M consecutive sub-carriers for a number Nconsecutive OFDM symbols where each symbol may also include a guardinterval or cyclic prefix. An OFDM air interface is typically designedto support carriers of different bandwidths, e.g., 5 MHz, 10 MHz, etc.The resource block size in the frequency dimension and the number ofavailable resource blocks are generally dependent on the bandwidth ofthe system.

In FIG. 2, the exemplary wireless terminal 200 comprises a processor 210communicably coupled to memory 220, for example, RAM, ROM, etc. Awireless radio transceiver 230 communicates over a wireless interfacewith the base stations of the network discussed above. The terminal alsoincludes a user interface (UI) 240 including a display, microphone andaudio output among other inputs and outputs. The processor may beimplemented as a digital controller and/or a digital signal processorunder control of executable programs stored in memory as is knowngenerally by those having ordinary skill in the art. Wireless terminals,which are referred to as User Equipment (UE) in WCDMA networks, are alsoreferred to herein as schedulable wireless communication entities, asdiscussed more fully below.

User equipment operating in a cellular network operate in a number of‘call states’ or ‘protocol states’ generally conditioned on actionsapplicable in each state. For example, in a mode typically referred toas an ‘idle’ mode, UE's may roam throughout a network withoutnecessarily initiating or soliciting uplink or downlink traffic, except,e.g., to periodically perform a location update to permit efficientnetwork paging. In another such protocol state, the UE may be capable ofinitiating network access via a specified shared channel, such as arandom access channel. A UE's ability or need to access physical layerresources may be conditioned on the protocol state. In some networks,for example, the UE may be permitted access to a shared control channelonly under certain protocol-related conditions, e.g., during initialnetwork entry. Alternatively, a UE may have a requirement to communicatetime-critical traffic, such as a handover request or acknowledgementmessage, with higher reliability. In such protocol states, the UE may bepermitted, either explicitly by the network, by design, or by acontrolling specification, such as a 3GPP specification, to adjust itsmaximum power level depending on its protocol state.

Generally, a wireless communication network infrastructure schedulingentity located, for example, in a base station 110 in FIG. 1, allocatesor assigns radio resources to schedulable wireless communicationentities, e.g., mobile terminals, in the wireless communication network.In FIG. 1, the base stations 110 each include a scheduler for schedulingand allocating resources to mobile terminals in corresponding cellularareas. In multiple access schemes such as those based on OFDM methods,multi-carrier access or multi-channel CDMA wireless communicationprotocols including, for example, IEEE-802.16e-2005, multi-carrierHRPD-A in 3GPP2, and the long term evolution of UTRA/UTRAN Study Item in3GPP (also known as evolved UTRA/UTRAN (EUTRA/EUTRAN)), scheduling maybe performed in the time and frequency dimensions using a FrequencySelective (FS) scheduler. To enable FS scheduling by the base stationscheduler, in some embodiments, each mobile terminal provides a perfrequency band channel quality indicator (CQI) to the scheduler.

In OFDM systems, a resource allocation is the frequency and timeallocation that maps information for a particular UE to resource blocksas determined by the scheduler. This allocation depends, for example, onthe frequency-selective channel-quality indication (CQI) reported by theUE to the scheduler. The channel-coding rate and the modulation scheme,which may be different for different resource blocks, are alsodetermined by the scheduler and may also depend on the reported CQI. AUE may not be assigned every sub-carrier in a resource block. It couldbe assigned every Qth sub-carrier of a resource block, for example, toimprove frequency diversity. Thus a resource assignment can be aresource block or a fraction thereof. More generally, a resourceassignment is a fraction of multiple resource blocks. Multiplexing oflower-layer control signaling may be based on time, frequency and/orcode multiplexing.

The interference impact of a network entity, for example, a schedulablewireless communication terminal, to an uncoordinated adjacent bandentity, referred to as the victim, is shown in FIG. 3. Victim entitiesmay be base stations or mobile terminals in immediately adjacent bandsor in non-contiguous adjacent bands, all of which are generally referredto as neighboring bands. The victim receiver may operate on or belong tothe same or different technology as the network entity producing theinterference. The victim receiver may also operate on or belong to thesame or different network types managed either by the same (coordinated)operator or by a different (uncoordinated) operator. The victim receivermay also operate on belong to a different technology network where thereis no coordination between networks to reduce interference.

Regional or international spectrum regulatory authorities frequentlydesignate contiguous segments of radio frequency spectrum, or radiobands for use by specific duplexing modes, for example, frequencydivision duplexing (FDD) or time-division duplexing (TDD) or by specificwireless technologies, such as Group Special Mobile (GSM), Code DivisionMultiple Access (CDMA), Wideband CDMA, etc. For example, GSM networksare frequently granted access to the so-called GSM 900 MHz (or PrimaryGSM) band specified as the frequency-duplex pair of band between thefrequencies 890-915 MHz and 935-960 MHz. This information may be storedin the UE or transmitted by the network controlling a UE in order topermit an optimum choice of PA output power back-off (also referred toas a power de-rating) or more generally to optimally adjust the maximumpower level of the PA conditioned on adjacent channel interferenceoffered to, and consistent with, the known adjacent channeltechnologies.

More generally, a frequency band adjacent to such a UE may be known fromnational or international regulations or from general deploymentcriteria, such as ‘licensed’ or ‘unlicensed’ designations to be subjectto specific maximum levels of interference from the band in which the UEis operating. When this information is stored in the UE or madeavailable by signaling from the network, the UE may optimize itsradiated power level subject to the known adjacent band interferencelimits.

In FIG. 3, a schedulable entity A1 306 is scheduled aperiodically.Particularly, the entity A1 is allocated radio resources includingbandwidth on carrier j 310 as well as bandwidth location in the carrierj band. The entity A1 is also allocated its transmission powerassignment or power adjustment and a scheduling grant by the basestation scheduling entity A1 302, which is part of network A.Schedulable entity A1 306 transmits using its assigned bandwidth oncarrier j 310 when scheduled by BS scheduling entity A1 302 and createsout of band emissions which impinge upon other carriers including anadjacent carrier j+k and is seen as interference 312 by BS schedulingentity B1 304, which is the victim receiver or entity, resulting inreduced SNR when receiving a scheduled transmission from schedulableentity B1 308 on carrier j+k 314. Since base station entity B1 304 ispart of Network B and there is no coordination, or sub-optimalcoordination, between Network A and Network B then it may not bepossible for scheduling entities like 306 and 308 to avoid mutualinterference.

In FIG. 3, the degree to which schedulable entity A1 306 interferes withschedulable entity B1 308 on carrier j+k 314 is dependent on the radiofrequency (RF) distance (also referred to as path loss) between theschedulable wireless communication entity and the other wirelesscommunications (victim) entity. The interference is also dependent onthe effective radiated power level of the transmitter, the size andamount of separation of the bandwidth allocations between entities andthe amount of overlap in time. Out of band emissions of one transmitterwill have smaller impact on another receiver if the path loss betweenthe transmitter and victim receiver is larger, and the impact will belarger if the path loss is smaller. Adjacent channel interference isalso present in TDD systems where both the BS 302 and schedulable entity306 of Network A transmit on the same carrier 310 and both BS 304 andschedulable entity 308 of Network B transmit on the same carrier 314 andhence both BS 302 and schedulable entity 306 cause out of band emissionsand hence interference 312 to adjacent carrier 314.

In one embodiment, the radio resource allocated to a schedulablewireless communication entity is based on an interference impact of theschedulable wireless communication entity operating on the radioresource allocated. The interference impact may be based on any one ormore of the following factors: a transmission waveform type of theschedulable wireless communication entity; a maximum allowed and currentpower level of the schedulable wireless communication entity; bandwidthassignable to the schedulable wireless communication entity; location ofthe assignable bandwidth in a carrier band; radio frequency distance(path loss) relative to another wireless communications entity;variation in the maximum transmit power of the schedulable wirelesscommunication entity for the assigned bandwidth; separation of assignedband relative to the other wireless communication entity; receptionbandwidth of the victim entity, minimum SNR required for operation ofthe victim entity; and reception multiple access processing (e.g. CDMA,OFDM, or TDMA), among other factors. The variation in the maximumtransmit power includes de-rating or re-rating the maximum transmitpower of the wireless communication entity as discussed further below.

For a given carrier band and band separation, transmissions with largeroccupied bandwidth (OBW) create more out of band emissions resulting ina larger adjacent or neighbor channel leakage ratio (ACLR) thantransmissions with smaller OBW. The increase in out of band emissionsfrom transmissions with larger OBW is due largely to increased adjacentchannel occupancy by 3^(rd) and 5^(th) order intermodulation (IM)products. The 3^(rd) order IM product largely determines ACLR inadjacent bands. The 5^(th) order IM product plateau largely determinesACLR in more distant (non-contiguous adjacent) bands. Note, however thatin networks such as IEEE 802.16e-2005 and 3GPP LTE networks whichsupport multiple bandwidth types, the dimensions in frequency of theadjacent band would also control such relationships. To avoid therelative increase in ACLR due to larger OBW, it is generally necessaryto reduce or de-rate transmission power created by the interferingentity in proportion (although not necessarily linearly so) to theincrease in OBW. Given a reference OBW (OBW_(REF)) with a known (e.g. 0)power de-rating (PD_(REF)) needed to meet a specified ACLR, an occupiedbandwidth power de-rating (OBPD) can be defined for an arbitrary OBWrelative to the reference OBW. The OBPD can be obtained empirically butmay also be approximated mathematically by an equation such as:OBPD∝10·log₁₀(OBW/OBW_(ref))  (1)

Generally, the transmission power of the mobile terminal must be reducedby OBPD to keep adjacent channel power leakage and therefore ACLR thesame for a transmission with a larger OBW compared to one with a smallerreference OBW. The total power de-rating (TPD) needed to account forboth an occupied bandwidth power de-rating (OBPD) and a waveform powerde-rating (WPD) in order to meet a given ACLR requirement can berepresented by:TPD=f(OBPD,WPD)  (2)

Note that the function f(.) may, for example, be the simple summation ofOBPD and WPD. The WPD accounts for waveform attributes such asmodulation and number of frequency or code channels and can bedetermined empirically through power amplifier measurements or indicatedby a waveform metric such as the Cubic Metric (CM). The additional powerde-rating from OBPD (beyond WPD alone) generally means worse cell edgecoverage for wireless terminals unless mitigated. For example, atransmission with 4.5 MHz occupied bandwidth on a 5 MHz E-UTRA carrierwith a fixed 5 MHz carrier separation will have a larger measured ACLR(e.g., approximately −30 dBc instead of −33 dBc) with regard to theadjacent 5 MHz carrier than a transmission with only 3.84 MHz occupiedbandwidth. To reduce the ACLR back to −33 dBc requires an OBPD ofapproximately 0.77 dB (based on empirical measurements) which is closeto the 0.70 dB given equation (1) above based on OBW of 4.5 MHz andOBW_(REF)=3.84 MHz.

The cubic metric (CM) characterizes the effects of the 3^(rd) order(cubic) non-linearity of a power amplifier on a waveform of interestrelative to a reference waveform in terms of the power de-rating neededto achieve the same ACLR as that achieved by the reference waveform atthe PA rated power. For example, a UE with power class of 24 dBm cannominally support a rated maximum power level (PMAX) of 24 dBm. Inpractice, the UE's current, or instantaneous, or local maximum powerlevel is limited to the operational maximum power level given byPMAX−f(OBPD, WPD) where f(.) can, for example, be the simple summationof OBPD and WPD such that the operational maximum power level isPMAX−(OBPD+WPD). The difference between PMAX and the UE's current powerlevel after power control or after assignment of an arbitrary powerlevel less than PMAX is called the UE's power margin or power headroom.Scheduling can be used to reduce or avoid OBPD.

In one embodiment, the scheduler allocates the radio resource based onthe interference impact by assigning bandwidth based on power headroomof the schedulable wireless communication entity. Particularly, thescheduler finds a bandwidth size that reduces OBPD enough such thatoperational maximum power (PMAX−OBPD−WPD) does not limit current powerof the schedulable wireless communication entity.

A scheduler may control leakage into adjacent and non-contiguousadjacent bands by scheduling mobile terminals that are “close” to theserving cell in terms of path loss with bandwidth allocations thatoccupy the entire carrier band or a bandwidth allocation that includesresource blocks (RB's) that are at the edge of the carrier band (e.g., 5MHz UTRA or LTE carrier) since due to power control it is very unlikelythat such a terminal will be operating at or near to PMAX and thereforeunlikely that its current power level would be limited by theoperational maximum power. A scheduler may schedule terminals that havelittle or no power margin with bandwidth allocations that excluderesource blocks at the carrier band edge therefore reducing OBPD andreducing the likelihood of the terminal being power limited by theoperational maximum power. It is possible to preserve frequencydiversity for terminals assigned a smaller transmission bandwidth tominimize OBPD by using RB hopping over a longer scheduling time intervalcomposed of several frames. Signaling overhead may be reduced by usingpre-determined hopping patterns, or pre-defined logical physicalpermutations. A UE will determine the OBPD corresponding to itsscheduled or allocated bandwidth size and location of the allocatedbandwidth in the carrier band. The UE therefore computes an operationalmaximum power for every scheduled transmission to determine if thecurrent power level will be limited.

In some embodiments, the schedulable wireless communication entityobtains maximum transmitter power information based on the radioresource assignment from reference information stored on the mobileterminal. For example, the maximum transmit power information may beobtained from a look-up table stored on the wireless terminal.Alternatively, the maximum transmit power information may be obtained inan over-the-air message. Several examples of the relationship betweenthe radio resource assignment and the maximum transmit power adjustmentare discussed more fully below. FIG. 4 illustrates exemplary OBPDde-rating values.

A BS may execute such scheduling decisions not simply fromconsiderations of interference offered by a UE to frequency-adjacentBS's, but may also simultaneously optimise the performance of multipleUE's whose allocated resources are derived from a common set of carrierfrequency resources (possibly extending over more than one carrierfrequency). That is, the BS may optimizing its scheduling allocationsfrom consideration of the mutual interference offered between amultiplicity of UE's.

The power radiated into an adjacent frequency band by a UE, and thedistortion offered by a UE to a BS receiver (or other UE receiver in thecase of a TDD system) within the set of time-frequency resourcesallocated by the BS, is governed by several practical design criteriarelated to the implementation of mobile terminal transmitters, includingoscillator phase noise, digital-analog converter noise, power amplifier(PA) linearity (in turn controlled by power amplifier mode, cost, powerconsumption etc.), among others.

Generally, however, and in common with most non-linear transformationsexpandable in terms a polynomial power series, UE power amplifiers giverise to undesired adjacent band interference in broad proportion, for agiven PA design, to the mean power offered to the PA input. As aconsequence of 3^(rd) or 5^(th) order polynomial terms, the frequency atwhich interference occurs is at 3 or 5 times the frequency of the inputsignal components, or harmonics thereof. Also, the power of suchout-of-band components generally increases at 3 or 5 times the rate ofincrease of the input power level.

Accordingly, mobile terminals may control their out of band emissionlevels by limiting the power to the PA. Given a specific rated maximumoutput (or input) power level designed to achieve a given level ofinterference into an adjacent frequency band, or level of in-banddistortion, a mobile terminal may elect to adjust, for example, reduceits input power level in order to reduce such unwanted effects. Asdescribed elsewhere herein, a decision to increase or decrease the inputor output PA power may be subject to other criteria, including waveformbandwidth, location in a frequency band, waveform quality metric, amongothers.

Generally, attributes of the waveform entering the power amplifier,along with attributes of network or UE operational parameters (such asthe desired level of out of band emissions, in-band distortion, or othercriteria described herein) are input to a controller which executes apre-defined power adjustment function, or de-rating function ƒ(x1, x2,x3, . . . , xN) which relates the attributes x1 etc. to a maximum powerlevel (where it is understood that de-rating may refer to a power levelin excess, or less than, a nominal or rated maximum power level).

In FIG. 6, a modulation and coding function 600 accepts an informationbit stream, such as higher layer protocol data units, and then appliestechniques such as forward error correction 601, modulation 609, andlinear and non-linear spectrum shaping 605 methods prior to frequencyconversion 607 and input to a PA 608. A controller 603 may derivewaveform attributes from the configuration of the modulation and codingfunction 600 or from direct observation of the signal immediately priorto frequency conversion 607. The controller 603 may also deriveoperational attributes from stored parameters or parameters signaled bythe network. The controller 603 then uses the waveform attributes, whichmay include signal bandwidth, frequency location, among others, plus theoperational attributes such as operational band, adjacent technologyamong others, to adjust the permitted maximum PA power value 605 whichis offered as a control metric to the PA 608.

In one embodiment, the radio resource allocated to a schedulablewireless communication entity is based on a maximum power available tothe schedulable wireless communication entity for the radio resourceallocated along or in combination with other factors, for example, theinterference impact. For a particular radio resource allocation, thescheduler knows the maximum transmit power of the correspondingschedulable wireless communication device. The scheduler may thus usethis information to manage the scheduling of schedulable wirelesscommunication entities, for example, to reduce interference.

In some embodiments, the scheduler determines a bandwidth size of theradio resource and allocates determined bandwidth to the schedulablewireless communications. The scheduler may also determine where within acarrier band the assigned radio resource is located. In one particularimplementation, the scheduler allocates bandwidth nearer an edge of acarrier band when the schedulable wireless communication entity requiresless transmit power, and the scheduler allocates bandwidth farther fromthe edge of the carrier band when the schedulable wireless communicationentity requires more transmit power. These allocations of course maydepend on the interference impact, for example, the proximity ofneighboring carrier bands among other factors discussed herein. Inanother implementation, the scheduler allocates a radio resource to theschedulable wireless communications entity nearer an edge of a carrierband when a radio frequency distance between the schedulable wirelesscommunication entity and the other wireless communications entity islarger, and the scheduler allocates the radio resource to theschedulable wireless communications entity farther from the edge of thecarrier band when the radio frequency distance between the schedulablewireless communication entity and the other wireless communicationsentity is smaller.

FIG. 5 illustrates, for successive transmission time intervals or TTI's(frames) 508, resource allocations to UE1 502 that are centered in theallocable band about DC and allocations for UE2 504 and UE3 506 locatedat each band edge. FIG. 5 shows a carrier band of 5 MHz with 4.5 MHz ofallocable bandwidth in units of 375 kHz resource blocks (RB's) such that12 RB's span the entire 4.5 MHz. Adjacent carriers are on either side ofthe 5 MHz carrier and are typically separated by guard band. Out of bandemissions decrease more rapidly when band edge occupancy is reduced oravoided. Therefore, reducing the size of band centered allocations asshown by UE1 502 means OBPD also decreases more rapidly 510. If, forexample, two or more RB's at the band edge are not allocated then theOBPD may be less than 0. Out of band emissions (and OBPD 516) forallocations that include band edge RB's as shown for UE4 512 and UE5 514decrease more slowly as the allocation is reduced compared to Bandcentered allocations. In the particular example shown, not until theoccupancy of a resource allocation with band edge RB's 512 UE4 dropsbelow ⅓ of the total allocable band does the OBPD drop below zero 518.

The BS may enhance its ability to optimally adjust the maximum permittedpower level of UE's under the control of the BS by occasionallymeasuring the BS receiver noise power contribution arising from reducedtransmitter waveform quality among UE's. FIG. 7 a illustrates thismethod in more detail in the context of OFD transmissions, or moregenerally transmissions comprising multiple sub-carriers. Specifically,a UE is shown transmitting on a set of active frequency sub-carriers 701received at the BS receiver with a specific energy per sub-carrier Es1700 and with an associated signal-noise ratio Es1/Nt with respect to theBS receiver thermal noise power density Nt 702.

In FIG. 7 a, the waveform and hence frequency sub-carriers transmittedby the UE are also subject to impairments attributable to practicallimitations of the UE transmitter. Although such impairments generallyhave frequency dependency, they may be regarded, to a firstapproximation, as a frequency-invariant additive noise power spectraldensity shown, at reception by the BS receiver, as a noise power densityNe 703. Generally, the UE transmitter performance is such that thereceived noise density Ne due to transmitter impairments is received ata level sufficiently below the BS receiver thermal noise density Nt soas to lead to a negligible increase in the effective total receivernoise density, i.e., Nt+Ne=Nt.

In FIG. 7 b, when operating under specific conditions, for example, whenlocated at the edge of uplink cell coverage, it may be beneficial forthe UE to adjust its maximum transmitter power level so as to increasethe effective received energy per sub-carrier Es2 704. Due to thenon-linear nature of the power amplifier, this may give rise to aproportionally larger (in dB) increase in the received noise density Ne705 due to transmitter impairments, but if Ne remains at a level smallerthan Nt, a net benefit in sub-carrier signal-noise ratio can accrue.

In order to permit the UE to optimize the ratio of Es/Ne at thetransmitter, the BS may broadcast an indication of a) the BS receiverthermal noise density Nt, b) the received noise component Ne due to UEtransmitter impairments, or c) a combination, sum, or some function ofthose measures. The UE may then optimize its maximum transmitter powerlevel to optimize the sub-carrier signal-noise ratio. For example, ifthe UE had available, from downlink power measurements, for example, anestimate of the path loss between the BS and UE, the UE may select themaximum radiated power level such that the received energy persub-carrier and associated receiver noise power density Ne, due totransmitter impairments, is optimized. In support of this, the BS mayelect to schedule specific time-frequency instances, or measurementopportunities, where a known set of sub-carriers 706 or othertime-frequency resources are known to be absent. This permits the BSreceiver to measure the desired noise power statistic (say, Nt+Ne) asshown in FIG. 7 b.

The BS may also transmit to a specific UE (unicast), or broadcast over aspecific cell or cells or over the entire network a specified measure ofthe ratio, measured at the UE PA output, between the energy per activesub-carrier Es, and the equivalent noise power density in inactivesub-carriers. A UE receiving such an indication, via a common ordedicated control channel, would then a) adjust their maximum powerlevel such that the ratio Es/Ne is aligned with the specified broadcastor unicast value. Alternatively, the BS may also transmit an upper orlower bound on this ratio. Typically, the transmission on the controlchannel of such a measure would require quantization of the specifiedvalue or bound to an integer word of a number N of bits.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession and enabling those ofordinary skill to make and use the same, it will be understood andappreciated that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the inventions,which are to be limited not by the exemplary embodiments but by theappended claims.

1. A method in schedulable wireless communication entity thatcommunicates in a wireless communication network, method comprising:receiving a radio resource assignment; varying a maximum transmit powerof the wireless communication entity based on the radio resourceassignment.
 2. The method of claim 1, obtaining maximum power adjustmentinformation based on the radio resource assignment from referenceinformation stored on the wireless communication entity, varying thetransmit power of the wireless communication entity based on the maximumpower adjustment information obtained.
 3. The method of claim 1, varyingthe transmit power includes decreasing the maximum transmit power asbandwidth allocated to the wireless communication entity increases, andincreasing the maximum transmit power as bandwidth allocated to thewireless communication entity decreases.
 4. The method of claim 1,varying the transmit power includes decreasing the maximum transmitpower as the allocated radio resources are positioned in frequencycloser to an edge of a carrier band within which the radio resource isallocated, and increasing the maximum transmit power as the allocatedradio resources are positioned in frequency farther from an edge of thecarrier band within which the radio resource is allocated.
 5. The methodof claim 1, varying the maximum transmit power includes de-rating themaximum transmit power of the wireless communication entity.
 6. Themethod of claim 1, varying the maximum transmit power includes re-ratingthe transmit power of the wireless communication entity.
 7. The methodof claim 1, the radio resource assignment includes a time-frequencyresource, varying the maximum transmit power based on a waveform metricderived from the allocated time-frequency resource.
 8. The method ofclaim 1, varying the maximum transmit power of the wirelesscommunication entity based on distance to an adjacent carrier frequency.9. The method of claim 1, varying the maximum transmit power of thewireless communication entity based on a frequency band allocated to thewireless communication entity.
 10. The method of claim 1, varying thepower de-rating in accordance with adjacent frequency bands.
 11. Themethod of claim 1, varying the maximum transmit power of the wirelesscommunication entity in accordance with a wireless communicationtechnology deployed in a frequency band adjacent to a frequency bandincluding the radio resource allocated to the wireless communicationentity.
 12. The method of claim 1, varying the maximum transmit power ofthe wireless communication entity in accordance with a protocol stategoverning the schedulable wireless communication entity.
 13. The methodof claim 1, varying the maximum transmit power of the wirelesscommunication entity in accordance with the power headroom of theschedulable wireless communication entity.
 14. The method of claim 1,varying the maximum transmit power of the wireless communication entityaccording to an indicated noise metric broadcast by the network.
 15. Themethod of claim 1, varying the maximum transmit power according to ametric broadcast by network describing a bounding ratio of a mean powerlevel of occupied sub-carriers to a mean power level of unoccupiedsub-carriers.
 16. A wireless communication entity schedulable in awireless communication network, comprising: a radio receiver, the radioreceiver receiving a radio resource assignment information; a poweramplifier; a controller communicably coupled to the power amplifier, thecontroller varying a maximum transmit power of the wirelesscommunication entity based on the radio resource assignment informationreceiver by the radio receiver.
 17. The wireless communication entity ofclaim 16, the radio resource assignment includes a time-frequencyresource, the controller varying the maximum transmit power based on awaveform metric derived from the allocated time-frequency resource.